1. Field of the Invention
The invention relates to the field of the processing of images by multicore optical fibers, and more particularly to the processing of images obtained in microendoscopy by multicore optical fibers.
2. Discussion of Background
As is illustrated in FIG. 1A, a conventional multimode fiber has a core 1 and a shell 3. A multicore fiber is a bundle of fibers, in a merged and stretched state, which consequently forms a continuous assembly. The shell of each individual fiber is melted with the shells of adjacent cores. Accordingly, within a multicore fiber it is only possible to distinguish individual cores, the shells of the fibers being merged with each other.
FIG. 1B is a cross-sectional view of a multicore fiber, the cores 24 and shells 26 being grouped within a first sheath 28, for example made of silica, and a second sheath 30, known as the outer sheath or "black" covering. The external diameter D.sub.1 of the assembly can be, for example, approximately 200 to 500 .mu.m wide.
FIG. 1C is a larger scale view of portion 32 of the multicore fiber of FIG. 1B. As shown FIG. 1C, the cores 24 have cross-sections with a variable shape and of varying homogeneity. In particular, the diameter d of each core 24 (i.e., the greatest distance separating two points of the same core) varies between the individual cores. Typically d can vary, for example, between 3 and 4 .mu.m for cores within a multicore fiber. In addition, the average distance between individual cores 24 is not uniform and can vary, for example, from 3 to 3.5 .mu.m within a multicore fiber.
The notion of multicore fibers must be distinguished from that of multifibers which constitute an assembly or bundle of independent fibers placed jointly and optionally bonded at an end. The present invention also applies to multifibers. Multicore fibers and multifibers are used in imaging, particularly in the medical field. Endoscopy and in particular microendoscopy enables a practitioner to acquire information or images of an area within an object, such as organs of the human body, such as the stomach, lungs, heart, etc., by reflecting light off of the object and receiving the reflected light into multicore fibers or multifibers.
FIG. 2 shows an apparatus for performing an endoscopy or microendoscopy procedure, including light source 2 which is focused by a lens 14 into a light inlet guide 16. The light inlet guide 16 is typically connected to a plurality of optical fibers 8 and 10 located at the periphery of a multicore fiber 12. A light beam generated by light source 2 through lens 14 can thus be directed onto a zone of an object or organ 6 to be observed. The object or organ 6 reflects a radiation 18 to the inlet 20 of the multicore fiber 12. Since the multicore fiber 12 has a coherent bundle of individual cores, the multicore fiber 12 transmits the received light of an obtained image of the object or organ 6 in well-ordered manner to an outlet 22 of the multicore fiber 12. The image at the outlet 22 of the multicore fiber 12 corresponds to an image of the object or organ 6 formed at the inlet 20. Means for receiving the obtained object image, such as camera 34 or any other display means, and means for storing, analyzing and/or representing the image, such as computer 36 with display 37, and keyboard 38 can also be provided in conjunction with the above apparatus.
The above imaging procedure is described, for example, in A. Katzir, "Optimal Fibers in Medicine", Scientific American, vol. 260(5), pp 120-125, 1989, and "Optimal Fiber Techniques (Medicine)", Encyclopedia of Physical Science and Technology, vol. 9, pp 630-646, 1987. In practice, a multicore fiber like multicore fiber 12 of FIG. 2 can have approximately 700 to 10,000 cores for microendoscopic applications. To obtain an image using a microendoscope, a network of cores of the cores of the multicore fiber 12 transmit the reflected unprocessed object image. This network is constituted by almost circular regions, each corresponding to a core.
The practitioner or person examining an image obtained by microendoscopy or more generally obtained with the aid of a multicore fiber, can consequently not use the crude or unprocessed image obtained at the multicore fiber outlet and the image requires digital processing in order to obtain a usable image. R. Conde et al, "Comparative Measurements of Image Quality in Image Guides", Biomedical Optics '94, describes processing of a test image of a Ronchi grid obtained by a multicore fiber. However, R. Conde et al provides no information on a practical implementation of such processing which requires a large mass of image data to be processed (typically 512.times.512 pixels) from each image obtained by a multicore fiber.